tipc: Fix log buffer memory leak if initialization fails

Moves log buffer cleanup into tipc_core_stop() so that memory allocated
for the log buffer is freed if tipc_core_start() is unsuccessful.

Signed-off-by: Anders Kaseorg <andersk@ksplice.com>
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>